In crown and bridge prosthodontics, metal copings are conventionally used to form the understructure of a dental restoration such as a crown and/or bridge. The metal coping must provide the required structural strength and rigidity necessary for the restoration to resist the forces of mastication when chewing food. In a ceramic-to-metal dental restoration the metal coping is covered with a fired-on coating of porcelain or acrylic for purposes primarily of aesthetics. Desirably, the metal coping should also provide a biocompatible relationship with the gingival tissue at the margin of the dental restoration.
Traditionally the dental coping was formed from cast metal using a conventional casting operation. Over the past twenty years a substitute procedure using a base composition of metal particles to form the dental coping has been introduced to the dental profession and has become widely accepted as a replacement for the traditional cast coping. In this substitute procedure the base composition of metal particles is shaped and/or molded over a die into a desired configuration and then heat treated into a porous structure which forms the dental coping upon the incorporation of a filler material pursuant to a subsequent heat treatment operation. The addition of filler material is required to solidify the porous structure into a solid mass representative of the finished dental coping before placement of the dental coping in the mouth of the patient. The dental material of choice for forming a dental coping in this manner is “Captek”, a registered trademark of Precious Chemicals Inc., which is a composition comprising noble metal particles as taught and described in U.S. Pat. Nos. 4,742,861; 4,814,008; 4,990,394; 5,234,343 and 5,336,091 the disclosures of which are herein incorporated by reference.
As described in the aforementioned patents a dental coping is formed from a base material composition comprising a combination of high fusing temperature metal particles and low fusing temperature metal particles combined in a matrix which should preferably include a volatile binder. Other minor constituents may be included such as particles of activated carbon. The high and low fusing temperature metal particles are selected to provide a melting characteristic which lies respectively above and below the heat treatment temperature to which the metal composite is to be subjected for forming the dental coping. Accordingly, the low fusing temperature metal particles should have a melting temperature to cause the particles of low fusing metal to melt at or below the selected heat treatment temperature whereas the high fusing temperature metal particles should have a melting temperature above the selected heat treatment temperature so that they essentially will not melt during heat treatment. The volatile binder may be composed of a material such as dental wax which should vaporize during heat treatment. The heat treatment process may involve more than one heat treatment step using different heat treatment temperatures or may involve use of a graduated temperature. In this instance the high and low fusing temperature metal particles are still distinguished from one another by the fact that the low fusing temperature metal particles should all melt during heat treatment whereas the high fusing temperature metal particles essentially do not melt during heat treatment. Since heat treatment occurs over a given time interval which is variable little or no melting of the high fusing metal particles should occur despite the selected time interval of heat treatment or the porous structure formed during heat treatment will shrink and result in failure.
Although this relatively new dental material and procedure for forming a dental coping has received wide acceptance in the dental profession a considerable amount of expertise is presently required of the dental laboratory technician or dentist in using the material to properly shape the material on the die particularly at the margin and to heat treat the material. The necessity to acquire such expertise has inhibited many laboratories and single practitioners from using this material and procedure on a consistent basis. Obviously, a dental material which would require less expertise for forming the dental coping would increase the desirability for using such material in the preparation of a dental restoration and/or to repair existing restorations.
The dental composition of the present invention is a modification in the formulation of the matrix of metal particles taught in the aforementioned patents and represents a substantial improvement in that the material composition of the present invention allows the material to be shaped and heat treated with much less expertise and little or no follow up supervision.